If you look in the G2 forum you'll see a post for fix for white lines I believe. The problem seems to happen when the software for a different panel ( LG used two different panels over the G2 ) putting the wrong one on appears to do this. Was pretty common for a while when it was first discovered.
However if a factory upgrade caused that to happen, talk to Warranty about it. They were awesome at helping me even being rooted and therefore technically out of warranty.